In recent years, efforts have been focused on developing a short wavelength semiconductor laser for the purpose of its application to high-density optical disk recording and the like. A nitrogen-containing hexagonal compound semiconductor such as GaN, AlGaN, InGaN, InGaAlN and GaPN (hereinafter, simply referred to as a nitride semiconductor) is used for the short wavelength semiconductor laser.
With rapid increase of communication traffic accompanying explosive spread of the Internet, expectations for not only optical communication technologies enabling high-speed and large-capacity communications, but also a high-speed transfer and large-capacity optical disk, and a highly-efficient optical device such as an LED light emitting element have been significantly grown. For example, an element on which two different semiconductor lasers are mounted to support both a CD-Rewritable method and a DVD-Rewritable method, and a double wavelength semiconductor laser to support multiplex communications have actively been developed.
Under these circumstances, as described in Patent Document 1, there is proposed a semiconductor light emitting device in which an n-GaN buffer layer is formed on a substrate; by using this n-GaN buffer layer as a common semiconductor layer, an n-type semiconductor layer, an active layer and a p-type semiconductor layer of each of the double wavelength light emitting elements are laminated on the n-GaN buffer layer; and a p electrode and an n electrode of each light emitting element are disposed opposite to each other across the substrate.
Moreover, a monolithically integrated light emitting element lasing with double wavelengths is manufactured for the semiconductor light emitting device described in the Patent Document 1. Hexagonal nitride semiconductor layers are formed on the main surface of the semiconductor substrate so that the semiconductor lasers have a planar surface parallel to the main surface of the substrate and also have a sloping surface inclined from the main surface, respectively. Subsequently, active layers are epitaxially grown on the planar and inclined surfaces of the semiconductor layers, so that the active layers containing In at composition ratios different from each other are formed to enable laser with double wavelengths.